The invention relates generally to inertial confinement fusion targets and more particularly to cryogenic targets for laser fusion.
High gain inertial confinement fusion (ICF) targets include condensed deuterium tritium (DT) fuel layers on the interior of a shell in a fuel capsule. These targets can be achieved at cryogenic temperatures, and the fuel layer may be either solid or liquid. Ideally, such a target should have a condensed fuel layer which is uniform and smooth, typically up to several hundred microns in thickness. However, in practice, such a fuel capsule is difficult to fabricate. The action of gravity causes the DT to slump while liquid, producing a sagged non-uniform layer. Gravitational slumping of the layer is a problem even if the final configuration is a solid layer, since it must pass through the liquid state as it cools.
U.S. Pat. Nos. 4,221,186 and 4,190,016 describe methods of forming cryogenic targets using a heat pulse in a freezing cell or cold gas jets, respectively. These methods, however, do not address the problem of gravitational slumping of the cryogenic layer.
A number of approaches to fabricating thick, homogeneous, cryogenic shells have been suggested, including: fast refreeze, refreeze in zero gravity, vibration centering inside a solid shell, inhomogeneous static electric field centering, thermal gradient centering, layer healing via distillation from self heating, cryogenic hemishell formation and assembly, and the application of droplet generator technology. All these methods appear to be long-term, high risk and expensive.
Other laser fusion target designs have utilizied foam layers. U.S. Pat. No. 4,012,265 shows a low density microcellular foam and metnod of making same which may be used to encapsulate a laser target, i.e., the foam is outside the fuel. U.S. Pat. No. 4,092,381 discloses a laser fusion target comprising a porous foam of deuterated hydrocarbon material, particularly deuterated polyethylene. Neither of these targets include a cryogenic layer of DT and neither address the problem of gravitational sagging.